fkie_cve-2021-46988
Vulnerability from fkie_nvd
Published
2024-02-28 09:15
Modified
2024-12-26 15:01
Summary
In the Linux kernel, the following vulnerability has been resolved: userfaultfd: release page in error path to avoid BUG_ON Consider the following sequence of events: 1. Userspace issues a UFFD ioctl, which ends up calling into shmem_mfill_atomic_pte(). We successfully account the blocks, we shmem_alloc_page(), but then the copy_from_user() fails. We return -ENOENT. We don't release the page we allocated. 2. Our caller detects this error code, tries the copy_from_user() after dropping the mmap_lock, and retries, calling back into shmem_mfill_atomic_pte(). 3. Meanwhile, let's say another process filled up the tmpfs being used. 4. So shmem_mfill_atomic_pte() fails to account blocks this time, and immediately returns - without releasing the page. This triggers a BUG_ON in our caller, which asserts that the page should always be consumed, unless -ENOENT is returned. To fix this, detect if we have such a "dangling" page when accounting fails, and if so, release it before returning.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/07c9b834c97d0fa3402fb7f3f3b32df370a6ff1fPatch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/140cfd9980124aecb6c03ef2e69c72d0548744dePatch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/2d59a0ed8b26b8f3638d8afc31f839e27759f1f6Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/319116227e52d49eee671f0aa278bac89b3c1b69Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/7ed9d238c7dbb1fdb63ad96a6184985151b0171cPatch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/ad53127973034c63b5348715a1043d0e80ceb330Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/b3f1731c6d7fbc1ebe3ed8eff6d6bec56d76ff43Patch
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/07c9b834c97d0fa3402fb7f3f3b32df370a6ff1fPatch
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/140cfd9980124aecb6c03ef2e69c72d0548744dePatch
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/2d59a0ed8b26b8f3638d8afc31f839e27759f1f6Patch
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/319116227e52d49eee671f0aa278bac89b3c1b69Patch
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/7ed9d238c7dbb1fdb63ad96a6184985151b0171cPatch
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/ad53127973034c63b5348715a1043d0e80ceb330Patch
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/b3f1731c6d7fbc1ebe3ed8eff6d6bec56d76ff43Patch



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  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nuserfaultfd: release page in error path to avoid BUG_ON\n\nConsider the following sequence of events:\n\n1. Userspace issues a UFFD ioctl, which ends up calling into\n   shmem_mfill_atomic_pte(). We successfully account the blocks, we\n   shmem_alloc_page(), but then the copy_from_user() fails. We return\n   -ENOENT. We don\u0027t release the page we allocated.\n2. Our caller detects this error code, tries the copy_from_user() after\n   dropping the mmap_lock, and retries, calling back into\n   shmem_mfill_atomic_pte().\n3. Meanwhile, let\u0027s say another process filled up the tmpfs being used.\n4. So shmem_mfill_atomic_pte() fails to account blocks this time, and\n   immediately returns - without releasing the page.\n\nThis triggers a BUG_ON in our caller, which asserts that the page\nshould always be consumed, unless -ENOENT is returned.\n\nTo fix this, detect if we have such a \"dangling\" page when accounting\nfails, and if so, release it before returning."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, se resolvi\u00f3 la siguiente vulnerabilidad: userfaultfd: publicar p\u00e1gina en ruta de error para evitar BUG_ON Considere la siguiente secuencia de eventos: 1. Userspace emite un ioctl UFFD, que termina llamando a shmem_mfill_atomic_pte(). Contamos con \u00e9xito los bloques, usamos shmem_alloc_page(), pero luego copy_from_user() falla. Volvemos -ENOENT. No publicamos la p\u00e1gina que asignamos. 2. Nuestra persona que llama detecta este c\u00f3digo de error, intenta copiar_from_user() despu\u00e9s de descartar mmap_lock y vuelve a intentarlo, volviendo a llamar a shmem_mfill_atomic_pte(). 3. Mientras tanto, digamos que otro proceso llen\u00f3 los tmpfs que se estaban utilizando. 4. Entonces shmem_mfill_atomic_pte() no logra bloquear la cuenta esta vez y regresa inmediatamente, sin liberar la p\u00e1gina. Esto desencadena un BUG_ON en nuestra persona que llama, que afirma que la p\u00e1gina siempre debe consumirse, a menos que se devuelva -ENOENT. Para solucionar este problema, detectar si tenemos esa p\u00e1gina \"colgante\" cuando falla la contabilidad y, en caso afirmativo, liberarla antes de regresar."
    }
  ],
  "id": "CVE-2021-46988",
  "lastModified": "2024-12-26T15:01:37.110",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "LOCAL",
          "availabilityImpact": "HIGH",
          "baseScore": 5.5,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 1.8,
        "impactScore": 3.6,
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
    ]
  },
  "published": "2024-02-28T09:15:37.640",
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  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-416"
        }
      ],
      "source": "nvd@nist.gov",
      "type": "Primary"
    }
  ]
}


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